The incorporation of additives in so-called "neat" thermoplastic polymeric host materials (that is, polymeric materials containing no additives) so as to achieve desired physical properties is well known. Thus, the art has conventionally incorporated colorants, stabilizers, delusterants, flame retardants, fillers, antimicrobial agents, antistatic agents, optical brighteners, extenders, processing aids and other functional additives into polymeric host materials in an effort to "engineer" desired properties of the resulting additive-containing polymeric host material. Such additives are typically added any time prior to shaping of the polymeric material, for example, by spinning or molding (e.g., extrusion, injection, or blow-molding) operations.
The incorporation of colorant additives in filaments formed by melt-spinning a polymeric material has presented unique challenges. For example, the amount of particulate pigment dispersed in a concentrate which is added to the polymeric material must be sufficiently high to impart satisfactory color density, but must not be so high as to interrupt the spinning process. One prior proposal for incorporating colorant additives in thermoplastic polymeric materials is disclosed in U.S. Pat. No. 5,236,645 to Frank R. Jones on Aug. 17, 1993 (the entire content of which is expressly incorporated hereinto by reference).
According to the Jones '645 patent, additives are introduced into a thermoplastic melt by feeding at least one additive in an aqueous vehicle containing a dispersant to form an aqueous additive stream to a vented extruder which is extruding a thermoplastic. The aqueous portion of the aqueous additive stream is thereby volatilized within the extruder and is removed therefrom via an extruder vent. As a result, a substantially homogeneous system containing the thermoplastic, dispersant and the additive is obtained which may thereafter be spun into a filament by melt-extrusion through filament-forming orifices in a spinneret associated with a spin pack assembly.
Although the techniques disclosed in the Jones '645 patent are entirely satisfactory, some further improvements to incorporating additives in a melt flow of thermoplastic polymeric materials would be desirable. For example, it would especially be desirable if the additive stream was non-aqueous as this would obviate the need for a vented extruder (i.e., since a volatilized aqueous portion of the additive stream would not then need to escape prior to melt-spinning). Furthermore, it is entirely possible that a non-aqueous additive stream could be introduced physically near or into the spin pack assembly where it can be mixed with a melt flow of the polymeric material immediately upstream of the spinneret orifices (and preferably downstream of the polymer filter section of the spin pack assembly) thereby bypassing the extruder. Such a possibility would then allow additive concentration and/or types to be changed on a continuous basis to produce sequential lengths of melt-spun filaments having desired, but different, properties and/or characteristics. That is, the upstream processing equipment, for example, the extruders and process piping, which supply the polymeric host material to the spin pack assembly would not necessarily need to be shut down for purposes of cleaning. Furthermore, by introducing a non-aqueous additive stream directly into the spin pack assembly, the flushing time would be relatively short thereby allowing, for example, quick color changes to occur from one filament production batch to another. It is towards providing such improvements that the present invention is directed.
Broadly, the present invention is embodied in a nonaqueous additive concentrate system for thermoplastic polymeric host materials which may be added directly to a melt flow of the polymeric material in metered amounts. More specifically, the additive concentrate system according to the present invention includes a filament additive which is dispersed in a liquid or liquefied nonaqueous carrier. The filament additive may, during use, be in the form of a solid particulate or a liquid. When a solid particulate is used, the additive system of this invention most preferably also includes a dispersant which coats the particulate additive. The additive concentrate system according to this invention is most preferably in the form of a flowable paste which can be added in metered amounts (dosed) to a melt flow of the polymeric material prior to being spun into filaments, for example near or into the spin pack assembly upstream of the assembly's filament-forming spinneret orifices.
In such a manner, therefore, synthetic filament batches having different additives may be produced sequentially on a continuous basis without costly equipment downtime. That is, the same spin pack assembly may be used to produce a first batch of filaments containing one type of additive during one production interval, and then used to produce a second batch of filaments containing a second type of additive during a succeeding production interval by changing the additive which is introduced into the filament-forming melt. Moreover, the time interval needed to change between different additives is relatively short since the additive system is most preferably introduced into the melt flow near or into the spin pack assembly which in turn reduces significantly the time needed to flush residual additive incorporated into the first batch of filaments. Production of different additive-containing filaments (e.g., filaments containing different colorants) is now possible in a relatively short period of time without stopping filament winding.
Thus, another aspect of this invention involves a method of continuously producing sequential lengths of different additive-containing filaments by continuously supplying a melt-spinnable polymeric host material to orifices of a spinneret and, during a first time interval, controllably dosing a concentrate system having one additive into the polymeric material to form a first polymeric mixture which is extruded through the spinneret orifices. Subsequently, during a second time interval, another concentrate system containing a different additive is controllably dosed into the polymeric material without disrupting the continuous supply of polymeric material to the spinneret orifices to form a second polymeric mixture which is extruded through the spinneret orifices.
During the change of additive concentrate, an intermediate time interval will be needed in order to flush the spinneret of residual amounts of the first additive concentrate. Thus, during the intermediate time intervals, an intermediate length of filaments will be produced which will change over the filament length from containing all of the first additive concentrate to containing all of the second additive concentrate. This intermediate length of filaments produced according to the present invention will be handled separately from the first and second lengths of production filaments. However, the amount of such intermediate length of filaments will be relatively small since, as noted above, the time interval needed to flush the spinneret of residual amounts of the first additive concentrate is relatively short.
Other advantages ensue from introducing the additive concentrate system to the polymeric host material within the spin pack assembly. For example, the spin pack assembly and its associated spinneret orifices may be so designed to form melt-spun multicomponent filaments (e.g., filaments having multiple domains of different polymer blends, colorants and/or other additives) such as those filaments disclosed in U.S. Pat. No. 5,162,074 to Hills (the entire content of which is expressly incorporated hereinto by reference) by splitting a melt-flow of polymeric host material into two or more subflows within the spin pack assembly. According to the present invention, therefore, the additive concentrate system may be introduced into the spin pack assembly and mixed with one or more of such subflows of polymeric host material without being mixed with other subflows so as to form multicomponent filaments. Therefore, while the discussion which follows emphasizes the production of filaments in which the additive concentrate system is substantially homogeneously mixed through the filament cross-section, it will be understood that the present invention is likewise applicable to the formation of multicomponent filaments whereby the additive concentrate system is substantially homogeneously mixed throughout one or more multiple polymeric domains in the filament cross-section without being present in the other domain(s) (e.g., as in core-sheath filaments, pie wedge filaments, side-by-side filaments and the like).
As noted above, significant processing flexibility ensues according to the present invention. Processing flexibility is the result of at least two features of the present invention. First, additive concentrate systems can be mixed above the spinneret with either the entire host polymer or only a portion of the host polymer. For example, a functional additive (e.g., an antistatic agent) concentrate system might be mixed with only a third of the host polymer such that a third of the filaments spun contain the antistatic agent and the remaining two-thirds do not.
Second, two or more additive concentrate systems can be mixed with the host polymer above the spinneret to achieve a single attribute in the fiber that is spun. For example, a yellow additive concentrate system and a blue additive concentrate system can be concurrently mixed with host polymer above the spinneret to provide a green fiber when the mixture is spun. There is no theoretical limit for the number of additive concentrate systems that can be mixed with the host polymer above the spinneret. The number of additive concentrate systems is limited only by the space available to inject the systems into the line. It is contemplated that the host polymer might also contain some additive prior to mixing above the spinneret.
These two features of the present invention are not mutually exclusive and great flexibility ensues from combining them. Using color as an example, either single color or multicolor yarn can be spun using the present invention. Single color yarn may be spun by mixing one or more color additive concentrate systems (e.g., a yellow system and blue system as exemplified above) with the entire host polymer such that a one color yarn (e.g., a multifilamentary yarn containing only green filaments) results.
Multicolor yarn (e.g., heather yarn) may be spun by selectively coloring separated portions of the host polymer and keeping each separated portion segregated until spun. For example, a portion of the host polymer might be colored with both the yellow and the blue additive systems to produce green filaments. Another portion of the host polymer might be colored with a red additive system to produce red filaments which are spun concurrently with the green filaments. The resulting multifilamentary yarn will therefore exhibit a heathered color due to the combination of individual red and green filaments present in the yarn.
The concepts above apply also to the spinning of filaments having multiple cross-sectional domains, such as core-sheath filaments, pie wedge filaments, side-by-side filaments and the like. Thus, for multidomain filaments, the additive concentrate system may be mixed with one or more split flows of the host polymer and then recombined with the remainder of the host polymer flow to achieve filaments having the additive present only in one or more of the cross-sectional domains.
When the additive is a colorant, therefore, a virtually unlimited number of multicolored, multidomain filaments can be produced. For example, only the core of a core-sheath filament may include one or more colorant additives which imparts to the fiber a color attribute that is visibly perceptible through the uncolored sheath. In this regard, it has been found that colorant additive(s) contained only in the core of a core-sheath multidomain filament results in a color intensity that is achieved with reduced colorant loading levels (e.g., between about 5 to about 10% less) as compared to filaments having the same colorant additive(s) homogeneously dispersed throughout the entire filament cross-section to achieve comparable color intensity.
Alternatively or additionally, the colorant additive may be present in the sheath of a core-sheath filament so as to achieve a color effect that is a combination of the core and sheath colors. Thus, by selectively choosing and incorporating colorants into the core and/or sheath, virtually any color attribute can be achieved for the resulting filament. Some particular combinations of colorants in both the core and sheath of a core-sheath filament may not necessarily result in a "pure" color combination of such colorants being realized for the filament. That is, the additive/subtractive effects of colorants in the core and sheath of core-sheath filaments are relatively complex and sometimes cannot be predicted with absolute certainty. However, routine experimentation with colorants in the core and/or sheath of core-sheath filaments will result in virtually an unlimited number of desired filament color attributes being obtained.
Other multiple domain filament combinations are envisioned, such as side-by-side domain filaments having different color attributes in each of the sides or pie wedge filaments whereby one or more of the wedges have the same or different color attributes. Such multiple domain filaments may be usefully employed to form heather yarns since the color additive-containing domains will visually present themselves at different locations along the length of the filaments when twisted (e.g., as may occur during yarn processing). Furthermore, the colorants and domains in which such colorants are present can be selected to achieve filaments which macroscopically appear to be uniformly colored.
Furthermore, although the additive concentrate systems of this invention may be metered (dosed) into the host polymer (whether in its entirety or in one or more of its split flows) at a substantially constant rate, periodic continual variance of the dose rate is also envisioned. Thus, as noted briefly above, when changing from one filament recipe to another, one or more of the additive concentrates will need to be varied in order to switch filament production from a former recipe to the then current recipe. A random or constant dosage rate variance can also be practiced, however, in which case the resulting filaments will have more or less of the additive distributed along its length. When the additive is a colorant, such a technique allows filaments to be formed having a slub-like color appearance along its axial length which may be employed, for example, to produce yarns having a striated or marbled impression.
These and other aspects and advantages of this invention will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.